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What is Mysimba?

Mysimba is a prescription weight-loss treatment. Each tablet contains 8 milligrams of naltrexone hydrochloride and 90 milligrams of bupropion hydrochloride.

It is available for those over the age of 18 who have a body mass index (BMI) of 30 or more. Alternatively, if you have a BMI of 27 to 30 and suffer from weight-related ailments, like high cholesterol, high blood pressure (hypertension) or type 2 diabetes, you can be prescribed Mysimba.

Please note, this medication should be taken with a reduced-calorie diet and regular exercise regime.

How does it work?

The active ingredients of Mysimba (bupropion and naltrexone) work by altering the way the brain interprets hunger. Their combined effect reduces hunger pains and food cravings, as well as reducing the effects of the part of the brain that associates pleasure with food. These effects reduce your appetite whilst simultaneously increasing your energy expenditure - the energy used to maintain breathing, blood circulation and digestion. It helps you stick to a calorie-controlled diet and lose weight. They come in the form of prolonged-release tablets, meaning effects are released into the body gradually across several hours.

It is still important to have a healthy diet and do regular physical activity whilst taking Mysimba to see the effects. If you are unsure if your diet is healthy, and do not know what exercise is appropriate for you to do, please speak with a doctor or health professional - they will be able to advise what is best.

It is also important to note, not all weight gain is a result of increased appetite. Psychological factors, such as anxiety and stress, can also play a part. For this reason, you should consult with your doctor before starting this medication - to determine the cause of your obesity.

How effective is it?

Clinical trials have been conducted to measure the effectiveness of Mysimba versus a placebo (an inactive drug, sometimes known as a “sugar pill”) measuring percentage weight loss throughout 26 - 56 weeks of treatment. Several studies have found average weight loss was around 3.7 - 5.7% when taking Mysimba, whereas those taking the placebo had an average weight loss of 1.3% - 1.9%. A separate study, that was conducted alongside a 56 week course of intensive counselling, found an 8.1% average weight loss compared to 4.9% with the placebo. In addition, 30% of the participants who took the Mysimba in this study achieved a 10% weight loss.

It is evident that, with the right support, Mysimba can be an effective treatment for weight loss.

How do I take it?

Full instructions of how to take this medication will be detailed in the patient information leaflet. This will be sent with your order and is also available to view on the right of this page.

If you are unsure about any instructions, please consult your doctor.

Mysimba is relatively easy to take and requires you to increase the dose slowly over the course of four weeks:

  • Week 1: take one tablet once a day in the morning
  • Week 2: take two tablets every day, one in the morning and one in the evening
  • Week 3: take three tablets every day, two in the morning and one in the evening
  • Week 4 and onward: take four tablets every day, two in the morning and two in the evening

You should stop taking Mysimba if you have not lost at least 5% of your initial body weight after 16 weeks of treatment. If you have lost 5% or more, the medication is working effectively and you can continue.

You should only stop taking Mysimba once you have spoken to your doctor.

After 16 weeks, you should have your progress monitored by your doctor. Make sure to visit them at least once annually.

If you forget to take a dose, skip it and continue as normal. Do not take a double-dose to make up for a missed tablet.

The maximum recommended daily dose of Mysimba is two tablets taken twice a day. If you take too many tablets at once, you may be at risk of experiencing seizures. In this scenario, please seek immediate medical attention.

What are the possible side effects?

Mysimba is a prescription medication and all prescription medications pose a risk of side effects.

For a comprehensive list of side effects, please consult the patient leaflet. The most common side effects (may affect up to 1 in 10 people) include:

  • Nausea
  • Vomiting
  • Constipation
  • Headaches
  • Dizziness
  • Feeling shaky
  • Dry mouth and changes in the taste of food
  • Abdominal pain
  • Headache
  • Insomnia (reduce by avoiding dose at bedtime)
  • Excessive sweating
  • Irregular heartbeat
  • Tinnitus (ringing in the ears)
  • Hot flushes
  • Rash or itching

You may also experience differences in your mood, such as irritability, anxiety and even depression. This could potentially lead to more serious side effects including suicidal thoughts. If you experience any symptoms affecting your mental health including distressing thoughts, please seek immediate medical attention. Do not take these feelings lightly.

Mysimba also increases the risk of fits and loss of consciousness. This is a very rare side effect (up to 1 in 1,000 people). Fits can be more likely if you take too much, take some other medicines or are at a higher risk than usual of fits. If you experience fits, seek immediate medical attention.

If you believe you are experiencing an allergic reaction to this treatment, you should discontinue treatment and seek immediate medical attention.

What precautions should I take?

There are a number of conditions that preclude the use of Mysimba. If you are unsure if any of the following apply to you, please contact your doctor for clarification.

You should not use Mysimba if you have:

  • liver or kidney issues
  • uncontrolled high blood pressure
  • history of psychological issues
  • a brain tumour
  • alcohol dependency
  • any drug dependency
  • history of seizures
  • history of head trauma

Excessive alcohol use can increase the likelihood of fits with this medication. If you drink heavily, consult your doctor before starting this treatment. You should gradually reduce how much you drink if you are taking Mysimba. Stopping suddenly can also increase the risk of fits.

If you are pregnant, breastfeeding or trying to conceive, do not take this medication.

You should be cautious if you are aged over 65, and you should not take Mysimba if you are over 75 years of age.

Mysimba can cause dizziness when patients first start treatment. It has also been known to cause seizures. For this reason, you should first consider how you react before driving or operating machinery.

For further advice on what conditions preclude you from using Mysimba, please consult the patient leaflet.

Mysimba with other medicines

Mysimba should not be taken with monoamine oxidase inhibitors (medicines to treat depression or Parkinson’s disease). You must stop taking these medicines for at least 14 days before starting Mysimba. You also must not take any opioids or medicines containing opiates. These could be medicines to treat coughs and colds (such as dextromethorphan or codeine), opiate addiction (like methadone), pain (morphine and codeine), or diarrhoea (like paregoric). You must have stopped taking any of these medicines at least 7-10 days before starting Mysimba.

Your doctor will also more closely monitor your side effects if you take antidepressants, some steroids, antimalarials, some antibiotics, antihistamines, sedatives (medicines to help you sleep), medicines to treat high blood pressure and several others. For a full list of medicines that may interact, please consult the patient leaflet.

If you are not sure whether you take any of the medication listed, please consult your doctor before taking Mysimba.

What else can I do to help with weight loss?

Unfortunately, Mysimba is not suitable for everyone. However, there are lifestyle changes you can make as well as other treatment options available that can help you lose weight.

Diet and exercise

The combination of a healthy diet and exercise is usually the first step in treating many common conditions. Even with Mysimba and other weight loss medications, you still need to have a reduced-calorie diet and do regular physical activity for the medicine to work. There are many diets out there that claim to help you lose weight quickly, but they are not recommended by healthcare professionals and can have many side effects such as dehydration and mood swings. They can also have severe psychological risks. One study conducted in 2016 has found that those who try to follow extreme diets are 18 times more likely to develop eating disorders.

There are instead some simple steps that you can take that will set you on the path of a healthier diet and will ensure long-term success. You should aim to have a balanced diet of:

  • high-fibre grains, including: brown rice, bulgur, whole-grain pastas and breads and porridge
  • foods high in protein, including: lentils, legumes, fish and lean meat
  • a variety of leafy and starchy vegetables, including: spinach, rocket, carrots and beans
  • different types of fruit, including: apples, berries, pears and oranges
  • healthy oils and fats, including those from nuts, seeds, oily fish and vegetable oils

You should also try to limit simple carbohydrates (white bread, sweets), processed foods (crisps, ready meals) and saturated fats (bacon, full-fat dairy).

Exercise is also important, as you need to burn more calories than you intake in order to lose weight. The NHS recommends either 150 minutes of moderate activity, such as brisk walking, cycling, tennis or dancing, or 75 minutes of vigorous activity such as jogging, skipping or an intense sport. You should start by doing a few minutes of exercise each day until you gradually improve your fitness.

Consult with your doctor or a dietitian if you are not sure how to eat healthily and exercise. They will help you come up with a plan that works best for you and help you start your weight loss journey.


Xenical, often referred to by its generic form ‘orlistat’, is an alternate medication for weight loss and comes in the form of 120mg capsules. It works by reducing the amount of fat your body absorbs, breaking down nearly ⅓ of the fat you eat. The undigested fats that are not absorbed into your body are released into your stools. However, it is still recommended you maintain a healthy diet and exercise alongside taking Xenical. You will need to have a BMI of 30 or over (or 28 if you have other associated risk factors) and you will need to fill out a short consultation form before it can be prescribed. A lower dose of orlistat (60mg) can be bought over the counter in the UK after an assessment by a pharmacist.


Saxenda falls under a group of medicines called GLP-1 inhibitors but specifically contains liraglutide. It works by mimicking a hormone in your body called glucagon-like peptide (GLP-1), that promotes insulin production and glucagon secretion after you eat (when your blood sugar levels are high). This helps to suppress your appetite and manage blood glucose levels (although it is not intended for sole treatment of diabetes). Saxenda also slows movement of food from your stomach to your small intestine, making you feel full for longer. It comes in the form of injection pens that you must inject yourself with and is available through prescription only. You will need to have a BMI of 30 or over (or 28 if you have other associated risk factors) and fill out a short consultation form before it can be prescribed.

Weight Loss Surgery

Weight loss surgery, also known as bariatric or metabolic surgery, is an option for those who have been struggling to lose weight with other methods. It is available to those who have a BMI of 35 or over. If you are interested in weight loss surgery, speak to your GP who can refer you to a surgeon.

Can I buy Mysimba online?

Yes, you can buy Mysimba online. However, as a prescription medication, it is subject to strict prescribing guidelines. We require you to complete a consultation before you place your order. This is included in the overall price and is a way for our doctors to confirm the medication is safe to use.

The entire process, from order to delivery, should take no longer than 48 hours.

Note: You must complete a short online consultation so that our doctor can ensure that the treatment is suitable for you. The above pricing should only be used as a reference. The final decision to issue this treatment lies with the prescribing doctor.

Medically reviewed by Dr. Plauto Filho Written by our editorial team Last reviewed 04-10-2023
Mysimba information
Product nameMysimba
Active ingredient(s)Naltrexone/bupropion
ManufacturerOrexigen Therapeutics
Trustpilot rating4.4/5
Trustpilot reviews26
AvailabilityOut of stock
DescriptionMysimba is an effective weight loss treatment
ExemptionSubject to medical prescription
Available dosageProlonged-release tablets, 8mg naltrexone and90mg bupropion
ApplicationAdults who are obese (have a body-mass index of 30 or above) or who are overweight (have a BMI of 27 or above) and have certain weight-related health complications
UsageConsult patient leaflet
Drug classSerotonin and noradrenaline reuptake inhibitors/opioid receptor antagonists
Alcohol consumptionAvoid alcohol consumption
When breastfeedingNot recommended, ask your doctor for alternatives
When pregnantNot recommended, ask your doctor for alternatives
Mysimba reviews
Box of Mysimba 8mg/90mg naltrexone/bupropion hydrochloride 112 prolonged-release tablets Excellent 4.4 26 patients have reviewed Mysimba on Trustpilot

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